The "Run One Program Only" Phenomenon

     As previously discussed,embedded devices normally embody the functionality they implement.In other words,they are designed to run one program(or just a few)with

 a predictable usage pattern. This is in clear contrast to general-purpose systems for which programs and usage are rarely known at design time and for which these 

parameters can only be inferred based on statistical  information about the install base.

     Nonetheless,the spectrum of variability in the general-purpose capabilities of an embedded device is quite broad,from truly single-function devices to completely 

versatile PDAS.In particular,the emerging ubiquitous networking infrastructure  is making it much more likely that devices will have multiple functions and more general-

purpose functionality . For example,the job of keeping up with networking  is itself  not a fixed task：protocols and standards evolve continuously and networking systems 

need programmability to avoid earlier-than-necessary obsolescence .Even  in areas for which networking was previously considered impractical or too expensive,new 

technologies are starting to bridge the gap.For example,Bluetooth(a short-range wireless protocol) is successfully attacking the domain of personal area networking.New 

generations of cellular technology(GPRS,2.5G,or 3G)are making transparent connectivity for non-interactive devices a reality,and between these two,medium-range 

standards such as 802.11 is becoming popular.

      Once devices become transparently connected network nodes,the operation of downloading a new program to them becomes much easier.This functionality is 

already  being used in various forms for diagnostics and accounting(vending machines)maintenance and upgrades(set-top boxes), or selective support of new 

algorithms (cellular base stations).

      In spite of  this,there are still many applications in which the"run one program only" phenomenon dominates. In these areas,radically new devices can sometimes turn

around quickly from concept to product,because of shorter development time opportunities.A device that runs only one application requires less system development than

a workstation with a new CPU or OS(operating system)because,for example,such single-program devices need not support legacy applications.

译文：

          正如之前所说的，嵌入式设备通常是实现某一单一功能。换句话说，他们通常用某一单独的程序来实现某一可以预见的功能。这和通用系统有着显著的区别，通用系统很少能在设计阶段明确程序和使用方法，许多参数只能通过使用时的统计信息加以推测。

          然而，嵌入式设备在通用功能的实现可变范围更加广泛，不管是单一功能的设备,还是多功能掌上电脑。尤其是新兴的无处不在的网络基础设施使得更多的设备具有多样的

功能和通用的功能。比如说：保持网络畅通是设备本身必须具备的功能，而不是其他的辅助设备的工作,涉及到连续网络系统的协议和标准需要可编程才能避免被很快的被淘汰掉。过去的时候甚至在有些地方人们认为网络不实用而且太贵，新的技术将致力于改变这一误解。比如说：蓝牙【一种短距离无线通信】就成功的应用于私人领域的网络连接。新一代的蜂窝移动通信技术（GPRS ,2.5G,或3G）使得非交互式设备之间的传输连接变为现实。在这两者之间，像802.11这种中距离的无线网络技术也变得流行起来。

        一旦设备之间能够通过网络节点进行传输连接，下载程序到设备中将变得很简单。 这项功能将会被广泛的应用在各种场合的诊断和计算【如自动售货机】或维护和升级【如机顶盒】，或者更新的算法提供更多的支持【如手机基站】。

       除了这些，这儿仍然有很多的“只运行单个程序”占主导地位的应用。在这些领域，由于更短的开始时间，一些新的设备有时能够很快的将一个概念转换为产品。那些只运行单一程序的设备需要更少的系统开发相比于基于中央处理器或者操作系统开发,比如需要更少的以往的应用程序。